What Is Anodizing
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. The process is called anodizing because the part to be treated forms the anode electrode of an electrolytic cell. Anodizing increases resistance to corrosion and wear, and provides better adhesion for paint primers and glues than bare metal does. Anodic films can also be used for several cosmetic effects, either with thick porous coatings that can absorb dyes or with thin transparent coatings that add reflected light wave interference effects. Anodizing is also used to prevent galling of threaded components and to make dielectric films for electrolytic capacitors. Anodic films are most commonly applied to protect aluminium alloys, although processes also exist for titanium, zinc, magnesium, niobium, zirconium, hafnium, and tantalum.
Advantages of Anodizing
Increased wear resistance
Aluminum oxide is a different material from the underlying raw aluminum. This material has a much higher hardness than aluminum. The hardness is so much higher that some anodizing processes result in the top layer of the aluminum having similar hardness to a hardened steel. When two materials come in contact, the softer material wears while the harder material remains undamaged. Thus this outside hard layer preserves the softer underlying aluminum from wear.
Increased corrosion resistance
The aluminum oxide layer created by anodization is largely inert, which means it doesn’t react with most chemicals. This lack of reactivity increases the corrosion resistance of an anodized part. One of the most common ways for aluminum to corrode is through galvanic corrosion. This reaction occurs when dissimilar metals come into electrical contact. For example, if an uncoated aluminum part has an uncoated steel fastener installed, the two will corrode in the presence of moisture.
Dimensional accuracy
While the anodizing process does impact the final dimensions of parts, it is a negligible amount for most applications. The thickest anodizing process, type 3 hard coat anodizing, only adds approximately one thousandth of an inch (0.001’’) to the thickness. Compare this to powder coating, which adds up to five thousandths to final dimensions.
Heat dissipation
Heat dissipation increases with surface area. When a part is anodized, the aluminum oxide structure creates microscopic pores. These small pores are what accept the dye, and also have the added benefit of increasing the surface area of the part, thus increasing heat dissipation.
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CNC Machining Parts Anodizing
CNC machining parts anodizing is a surface treatment process widely applied to CNC - machined components, especially those made of aluminum and its alloys. Add to Inquiry -
CNC Anodizing Aluminum Machining Parts
Anodizing is a common metal oxidation process, which can attach an oxide layer to the surface of the metal to increase its hardness, corrosion resistance and beauty. In our daily life, anodizing has Add to Inquiry -
Anodizing Machining Parts
Anodizing is electrochemical oxidation of metals or alloys. Aluminum and its alloy in the corresponding electrolyte and specific process conditions, due to the action of external current, the process Add to Inquiry
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We mainly engaged in a variety of precision machinery parts processing,CNC processing,CNC lathe processing, etc., the company set manufacturing, specialized, sales, after-sales service as one, processing precision parts are widely used in machinery manufacturing, oil mining, aviation military, precision instruments, medical, communication electronics, new energy, etc. Optics and other industries.
What Materials Can Be Anodized
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Aluminum
The most common materials to be anodized are aluminum and aluminum alloys. Because of its high strength-to-weight ratio and relative availability, aluminum is utilized extensively in industrial operations. Aluminum’s overall performance is enhanced, and its useful life is increased by anodizing. There are numerous distinct aluminum anodizing procedures.
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Magnesium
Magnesium is typically anodized for use as a paint primer, and for this application, thin coatings (as little as 5 m) are adequate. Magnesium materials can have their corrosion resistance improved by having anodic coatings that are thicker (25 m or more). For best results, these coatings need to be sealed with sodium silicate, wax, or oil.
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Titanium
The jaw, hip, and knee implants are frequently made of anodized titanium. In addition, anodized titanium is popular for art, costume jewelry, body piercing jewelry, and wedding bands because the anodizing technique may produce various hues without using dyes. The oxide layer’s thickness, ranging from 30 nanometers to several micrometers, affects color. The anodizing voltage, in turn, controls thickness.
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Niobium
Similar chemicals and procedures to anodizing titanium can be used on niobium. By altering the coating thickness, which is also reliant on anodizing voltage, a variety of colors can be produced. Costume and body jewelry, commemorative coins, and other highly attractive objects are frequently made of anodized niobium.
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Tantalum
needs to be anodized using a method similar to that of titanium and niobium. By adjusting the film thickness, a variety of appealing colors can be created. Depending on the chemical solution employed and the process temperature, the voltage needed to anodize tantalum typically ranges from 18 to 23 Angstroms per volt. The most popular type of tantalum used to make capacitors is anodized tantalum.
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Zinc
The process of anodizing zinc can be challenging. When used with voltages as high as 200V DC, a mixture of ammonium phosphate, chromate, and fluoride can create anodized coatings up to 80 m thick on zinc alloys, enhancing their hardness and corrosion resistance. Zinc-plated steel components can be anodized utilizing chemical baths comprising sodium silicate, sodium hydroxide, borax, sodium nitrate, and nickel sulfate at lower voltages (20-30V DC).
What Are the Types of Anodizing
Type I — chromic acid anodize
Of the three main types of anodizing, chromic acid anodizing (type i) produces the thinnest oxide layer, at 0.00002 to 0.0001 inches. When properly sealed, the oxide layer produced by chromic acid anodization provides aluminum with a similar level of corrosion resistance to the thicker layers produced by other anodizing methods, such as sulfuric acid or hard coat. Due to the coating layer being thinner, type I oxide coatings absorb less color when dyed, and the coating has a grayish cast. This grayish cast restricts the use of chromic acid anodizing as a decorative finish. Nevertheless, it is possible to dye a type I coating black and apply it as a protection for housings for optical components.
Type ii — sulfuric acid anodize
Type ii (sulfuric acid) is the most popular anodizing method. Films produced by the sulfuric acid anodizing technique have a thickness between .0002 and .001 inches. The oxide build-up changes the part's surface, making it well-suited for situations where abrasion resistance and hardness are necessary. The colorful surface finish on aluminum and related alloys is obtained by making use of the porosity of the sulfuric acid coatings before sealing. The porous aluminum oxide readily absorbs dyes. Sealing the anodic oxide film after the dye has been applied helps avoid color fading while the part is in use. Despite being generally colorfast, colored anodized films tend to fade in continuous exposure to uv light. Some color options available with this anodizing technique include black, gray, brown, red, blue, green, and gold.
Type iii — hard anodize or hard coat
Hard coat anodizing is typically applied using an electrolyte based on sulfuric acid. It produces a substantially denser and thicker oxide layer than sulfuric acid anodizing. The coating thickness of hard anodizing is typically between 0.0005 to 0.002 inches. The hard anodizing process is recommended for applications requiring superior abrasion resistance in corrosive environments. It can also be useful in cases where better electrical insulation is needed. Because type iii anodized coatings can be made quite thick, they are useful for refurbishing wear coatings or for remanufacturing out-of-spec components. Some key characteristics of hard anodized coatings include increased wear resistance compared to other types of anodized coating, electrically non-conductive surface, fixing aluminum's worn surfaces by creating a uniform layer across the surface, and enhanced lubrication for sliding applications. Hard coat anodizing can be used for valves and pistons, sliding parts, gears, joint swivels, electrical insulation, blast shields, and more.
What is Anodizing Used For
Anodizing is most commonly used for improved corrosion resistance on certain types of aluminum alloys. Aluminum alloys that are subject to marine environments typically benefit from anodizing. Ship hulls, dock components, and oil rig structures are common examples of these.
Anodizing is also used for abrasion control. Aluminum that has not been oxidized is a relatively soft material when compared with steel or titanium. Aluminum oxide, on the other hand, is an extremely hard material. In fact, aluminum oxide is often used in sandpapers because of its high hardness. When the anodizing process forms an aluminum oxide layer on the outside of an aluminum alloy, it greatly increases its wear resistance because aluminum oxide is such a hard material. Applications where anodizing is used for wear resistance include aluminum components that are subjected to constant movement and contact with other materials.
Dyeing is another popular application of anodized aluminum. The aluminum oxide layer that is created on an aluminum alloy during the anodizing process is porous. This allows some dyes to be absorbed by the oxide layer. Aluminum alloys that couldn’t be dyed before can now be made to be a variety of colors. Applications of dyeing anodized aluminum include artwork and and aluminum signs.
How Does Anodizing Work in Practice
Prepare the surface
Before you anodize a part, you have to prepare its surface through mechanical and chemical means. First, polish or bead blast the surface to ensure your part has the desired visual appearance. Bead blasting will give your part a natural matte finish, while brushing will give your part a brushed appearance. The chemicals you use prior to anodizing will influence the glossiness of your part. Etching, for instance, will give your part a smooth satin finish. For a glossy finish, you’ll want to go with bright dipping or chemical polishing. Next, rinse the part with deionized water and other solvents to remove impurities, including machining residues like oils and coolant. Place the rinsed parts in a chemical bath of sodium hydroxide (NaOH) and nitric acid (HNO3) to scour the top layer of the metal. If you’ve already treated the part mechanically, this step isn’t always necessary. You can also mask areas of a part to prevent an anodizing surface from forming there.
Anodize
Next, place the part or parts in the anodization bath, connected to the electrical circuit. Parameters can vary based on the desired properties described above, including the solution composition, temperature, current density, voltage and time.
Clean the parts
After anodization, you have to clean the part with deionized water and solvents. Don’t forget to dry the part after. This removes excess solution and readies the part for its chromatic finish.
Add color
You can control the color of the part during anodizing. The wavelengths of the visible spectrum of light, measured in nanometers, can reflect differently depending on the thickness of the oxide coating. Different parameters achieve a variety of colors. To give your part a bronze or black finish, immerse the part in a solution of metallic salts. These react with the surface to fill the pores with a black or bronze chemical compound. This process is called electrolytic coloring. If you want another color, you can use dip coloring, which fills the pores with a dye solution. After dipping your part in the dye, place it in heated DI water to halt any further reactions. Dip coloring is the least durable of the coloring options detailed here, as the color may degrade when exposed to UV light over time.
Seal the pores
After anodizing, you have to seal the microscopic pores on the surface of the part to prevent further corrosion and improve performance. Without sealing the pores, anodized parts may feel sticky to the touch. As well, open pores can collect dirt, contaminants and stains.
Considerations Before Anodizing
Not all materials can be anodized
Materials like steel will dissolve in the chemical solution and, therefore, can’t be anodized.
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Change in dimensions and tolerances
Geometric dimensions and tolerances may change due to the added coating, so you should account for it in the design process.
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Matching colour
Expect that colour matching will never be 100% accurate.
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Surface roughness
Surface roughness on the part can negatively impact the overall anodized finish.
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Out of reach areas
A portion of the part surface is likely to not become anodized during the anodizing process. The solution may not reach it, or it may not be completely submerged.
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Our factory
Shenzhen Tuohai Automation Equipment Co., Ltd. was founded in 2014, mainly engaged in a variety of precision machinery parts processing,CNC processing,CNC lathe processing, etc., the company set manufacturing, specialized, sales, after-sales service as one, processing precision parts are widely used in machinery manufacturing, oil mining, aviation military, precision instruments, medical, communication electronics, new energy, etc. Optics and other industries.Shenzhen Tuohai has Mazak five axis, CNC machining center, CNC lathe, turning and milling compound, milling machine, Japan Okamoto grinding machine and other kinds of production equipment more than 30 sets, three dimensional, two dimensional, height meter, hardness meter, marble inspection platform and other kinds of quality.
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